From DE 44 18 891 C2 there is known a drive system for a motor vehicle, with a first and a second driven axle, which drive system comprises an engine-gearbox unit and an axle drive block of a first driving axle with two differential drive stages and an output leading to the second driving axle. The first differential drive stage distributes the torque supplied by the engine-gearbox unit between a first driveshaft of the first driving axle and the second differential drive stage, and the second differential drive stage distributes its input torque between the second driveshaft of the first driving axle and the output to the second driving axle. A fluid friction coupling can be effectively inserted between the two driven axles. A further differential drive is used in the second driving axle in the form of an axle differential of the conventional type.
U.S. Pat. No. 6,296,590 proposes differential drives for use in motor vehicles with a primarily driven driving axle and an optionally driven driving axle, by means of which differential drives the optionally drivable driving axle can be connected and disconnected and by means of which, within the connected driving axle, starting from the open differential function, an increasing locking effect can be generated.